How To Avoid Ligthening Designing A Sailing Yatch

Discussion in 'Boat Design' started by metin_mehel, Apr 11, 2014.

  1. BertKu
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    BertKu Senior Member

    Yes, you are at the Great Lakes, it can be very scary there. I assume the 400 KA was measured there. Another reason why to ensure a low resistance and to measure it. You can see how the world has changed, we were only measuring 50.000 Ampere here 40 Years ago. Now they measure 400 KA, what will be measured in 20 years time?.

    He could create something like this as the secondary protection for himself, provided it is grounded with a separate thick cable to the ground plate.

    http://www.shieldingsystems.eu/userfiles/Image/EN/Faraday_tent_pyramid_shaped(1).jpg

    It is made from conductive material.
    Bert
     
  2. BertKu
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    BertKu Senior Member

    Hi Metin,
    Are you able to make a compartment in one of the hulls?? if so, why don't you get some material as per http://www.hollandshielding.com/158-EMI_RFI_shielded_Faraday_tent-en.htm and get a quote from them. You then place the conducting material in your hull in such a way that it is properly sealed and form a Faraday cage or you can buy a complete outfit as per website. You must still have a conductor from the top of the mast to the two ground-plates. You then wire your “sleeping bag” with a separate cable to one of the same ground plates. Trust me, if you do it properly, you will survive a direct lightning strike. The trick is to make sure that you have very low conductivity to the ground-plates and that your “suit”, “sleeping bag” or material properly glued against the inside of one of your hulls where you have made a compartment “just in case”. Just find out what the maximum current is what the material can carry for a few seconds. Bert. P.S. You will only carry secondarily induced currents
     
    Last edited: Apr 14, 2014
  3. SukiSolo
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    SukiSolo Senior Member

    Be wary of trying to use the aluminium in the mast as a conductor. Anodised aluminium is very poor as the anodising is a barrier to conductivity. I've been out on the Ijselmeer in strikes every 30 seconds or so and strangely enough the racing was abandoned. Other competitors saw a strike split into two about 10 meters (30') above my mast on the way into the harbour....

    Also had a strike on local Pond which although it did not directly hit anyone gave at least three sailors a good jump with light shock. It was raining very very heavily. Seen three guys get a shock from holding their shrouds whilst launcing off the beach - a woman walking her dog the other side of the Thames Estuary, some 7 mles away was killed by direct hit 20 minutes later.

    A Faraday cage will work pretty well but needs to be a decent conductive material and be careful of any galvanic corrosion ie do not fit brass or copper to aluminium without a proper insulator.

    I would imagine that one of Erics nice wooden or composite wing masts without stays (and if not carbon) would be pretty good at not exacerbating strike potential!.
     
  4. jonr
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    jonr Senior Member

    Once you have low electrical resistance, then it's all about the inductance of the grounding path. Combined with the rapid rise time of lightning, this is what allows voltages to get to damaging levels.

    Evidently there are anti-corrosion pastes that are to be used at the wire to mast connection point.
     
  5. ImaginaryNumber
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    ImaginaryNumber Imaginary Member

    Could larger diameter aluminum cable be substituted for the copper cable? Seems aluminum would be cheaper and lighter than copper, if aluminum is up to the task.
     
  6. PAR
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    PAR Yacht Designer/Builder

    Bert, welding wire (copper of course) isn't the best to employ. Solid core is the best, but prone to fatigue, so a heavy gauge triple twist is preferred and there are application specific versions of this type of wire, which uses much larger strands, than conventional wire and a whole lot more then welding wire.

    Other then conductivity with an alloy spar as the conductor (which generally sucks compared to a dedicated copper wire), the main issue is you'll be rigless after a strike. There's going to be rigging tangs and attachments that will literally blow off the mast, which kind of defeats the general idea of protection.

    Aluminum usually will vaporize in a good strike, along it's length someplace (typically at hard bends and attachment clamps), so the hit will arc and now you're back to square one.
     
  7. CDK
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    CDK retired engineer

    Wise words jonr !
    The rise time in a lighting hit is unimaginably short. Even massive solid copper conductors cannot channel a discharge unless the path is completely straight. A 90 degrees bend behaves like a quarter turn of a coil and may cause the discharge to take a shortcut rather than follow the conductor.

    Also, the often mentioned Faraday cage is highly overrated. If you think you have made a safe shelter against lightning, switch your cell phone on and check the signal level: anything above zero means the cage can be penetrated.
    Total protection can only be obtained well below the surface or in an armored vehicle like a tank.
     
  8. powerabout
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    powerabout Senior Member

    we need to mention to our non English speakers that many of the words that we use around boats are not English hence the strange spellings.
     
  9. jonr
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    jonr Senior Member

    Regarding inductance, the use of twisted pairs and/or a couple of loops will help keep lightning surges out of the wires you don't want it flowing in.

    Grounding straps (1.5" or wider) outperform wire due to "skin effect".

    TE-4 also supports using an aluminum mast as the ground conductor (no wire needed).
     
  10. powerabout
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    powerabout Senior Member

    Golden rule with lightning is there are no rules
     
  11. metin_mehel
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    metin_mehel mech.eng.

    I think l ll never go sailing in bad or possible bad weather as a result of this conversation lol. Thanks everybody. ..
     
  12. powerabout
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    powerabout Senior Member

    Golf is far more dangerous
     
  13. Navygate

    Navygate Previous Member

    But not nearly as much fun!
    :)
     
  14. ImaginaryNumber
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    ImaginaryNumber Imaginary Member


  15. BertKu
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    BertKu Senior Member

    Hi PAR,
    I went to Cape Town last week Tuesday and did not take my password for boat.net with me. Needless to say, I was unable to reply at an Internet place. I came back last night. We sold a couple of million different lightning protecting devices when I headed the electronic components division in Johannesburg and this drew me many times into problems with lightning and solutions to the craziest problems I encountered. Although lightning on the sea is slightly different then on the land, the damage was the same, except that the ground resistance varied more and if a place had two or a number of buildings, if the earth points in the ground was not properly connected to each other, one building would lift up in potential during a strike and needless to say that communications between the buildings were blown to pieces, due to the potential Voltage differences. This you don’t have at sea. The sea is one massive ground earth plate.
    While I was in Cape Town, I visited the Royal Yacht club and was surprised to see how some of the lightning (and the absence there off) protection was constructed. Quite a lot uses the aluminium mast and personally I am not too keen in using a higher resistance conductor for routing the lightning current from the top to the sea. When I lived in Johannesburg, I preferred to put a tennis court up on my property, instead of mowing the grass every week. One day I was closing the curtains, when a lightning strike hit the tennis court, some 8 meters away. Johannesburg is positioned some 2000 meters above the sea level and one of the hotspots in the world for lightning. Not only I was blinded for a long time and the secondary induced magnetic field gave me, as of a 20 pound hammer had hit my body. After I recovered, my thought went to my wife and daughter, who were closer to the tennis court (3 meter away), lying in bed in the bedroom. To my surprise they had not felt anything, I was puzzled. I suspected something and started to investigate and the builder told me that they used metal foil under the roof tiles and mesh wire every three layers of brick in the mortar. Also they had metal in the foundation, which was all connected to each other and earthed at various metal pins in the ground as earth points. A kind of Faraday cage thus. I had copper welding wire in the garage and made the following week-end a lightning conductor from it at the the tennis court. In view that crime was on the increase, I placed metal bars in front of the windows and connected them to the central earth connections. I have been hit many times since then, but never had any real problem anymore. However I used the blow torch and used plumbing solder on the copper wire to avoid oxidation and to stiffening the copper wire. Also I used metal strips attached to the court frame structure. That was the reason why I suggested using copper core of a thick 1000 Ampere welding cable; it is inexpensive and easy to obtain also for the reader in Turkey. But like you said, every action has a negative reaction and the rigging is a problem. I am thus a great believer in using a kind of Faraday cage to protect against secondary induced currents due to a lightning strike. For the primary lightning conductor, indeed copper is the best. To build a primary Faraday cage protection is thus an overkill and very difficult in the construction with all the wires and mast and other goodies on the deck. However I am flabbergasted why boat builders do not incorporate metalized sheeting or thin copper mesh wire in the GRP to protect the cabin. If the reason is, otherwise the WIFI and electronic devices will get smothered, fair enough, drop the idea. What about providing a type of metalized sleeping bag, plugged into the wall, connected to the central earth plate. It only need to discharge a few Ampere or a few hundred milli-Amperes to protect the crew against secondary induced currents and save their life’s. Provided they have incorporated the shortest and straightest lightning conductor from the top of the mast to the sea. (from copper)
    Bert
     
    Last edited: Apr 23, 2014
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